Relationship between fruit and seed traits and altitude in wild Prunus armeniaca

Abstract:【Objective】Prunus armeniaca Lam. is the world’s original population of cultivated apricots and also the dominant species in the wild fruit forests of the Tianshan Mountains. It plays an important role in maintaining the stability of wild fruit forest ecosystems and has important values of ecology and germplasm resources. Seed reproduction is the way of natural regeneration of P. armeniaca. Normal fruit and seed development is an important basis for obtaining new provenances. The adaptation of fruit and seed traits to the environment of vertically distributed P. armeniaca populations in the mountains at altitudes ranging from 1000 m to 1700 m on both sides of the Ili Valley in Xinjiang is still unclear. The natural regeneration of P. armeniaca is achieved through live reproduction, and fruit and seeds that can develop normally are an important basis for obtaining a renewed seed source. The habitat conditions of wild fruit forests are closely related to their distribution and growth. In order to investigate the influence of altitude on the fruit and seed appearance traits of P. armeniaca, the relationship between the development of sexual organs of P. armeniaca and their degree of determination was investigated, with a view to providing some theoretical references for the study on the ecological adaptations of survival and sexual reproduction of P. armeniaca.【Methods】The P. armeniaca forest in Tuergenxinghuagou, Xinyuan county, Xinjiang was selected as the research region from July to August 2021. In the mountainous areaof 1100-1500 m with concentrated distribution of P. armeniaca, ten sample plots were set up at an average interval of 100 m from low to high in an altitude gradient from Ⅰ to Ⅴ. The environmental conditions were monitored. Five sample trees were selected at each altitude with similar diameter at breast height and vigor, five fruits were picked from each tree from four directions of the canopy, 20 fruits were picked from each tree, and 100 fruits were picked from each altitude to observe the fruit and seed traits. Fruit weight, vertical diameter, transverse diameter, side diameter, fruit shape index, pulp thickness, lightness, red level, orange degree, hue angle, total color, a/b-value, firmness, soluble solids content, acid content, solid/acid ratio; fresh weight of seed, dry weight of seed, vertical diameter, transverse diameter, side diameter, seed yield rate were measured. Preliminary processing of the data was carried out using Excel 2019. One-way ANOVA was used to analyze the fruit and seed traits of the samples collected at different altitudes. Duncan’s multiple range test was performed when the results were significant at α = 0.05. Pearson correlation analysis method was used to analyze the correlation between the altitude and fruit and seed traits. Double-tail test was used for the significance test. p＜0.05 meant the significant difference, and p＜0.01 meant the extremely significant difference. Multiple regression analysis and path analysis were used to analyze the effect of altitude gradient on fruit and seed traits. The above analysis was performed with SPSS 19.0.【Results】The correlation coefficients of fruit and seed sizes of P. armeniaca decreased with increasing altitude, and the correlation coefficients of vertical diameter, transverse diameter and fruit weight were -0.775, -0.728 and -0.697, respectively, and the correlation coefficients of dry weight of seed, vertical diameter and fresh weight of seeds were - 0.659, - 0.645 and -0.608, respectively, all of which were highly, significantly and negatively correlated with the altitude gradient; the correlation coefficients of flesh color, fruit quality and seed yield increased with increasing altitude, and the correlation coefficients of soluble solids content, hardness and orange color increased with increasing altitude. The correlation coefficients for fruit flesh color, fruit quality and seed yield all increased with increasing altitude, and the correlation coefficients for soluble solids, firmness and orange degree were 0.680, 0.606 and 0.384, respectively, and the correlation coefficient for seed yield rate was 0.341, all of which were significantly and positively correlated with the altitude gradient. Further path analysis showed that the altitude gradient had the greatest direct effect on fruit and seed vertical diameter, with direct path coefficients being -0.616 and -0.406, respectively, and the greatest indirect effect on fruit solid/acid ratio and fresh weight of seed, with indirect path coefficients being 0.416 and -0.468, respectively. The analysis of the degree of determination showed that the change in altitude gradient mainly affected the vertical diameter, fruit shape index, soluble solids content, solid/acid ratio, hue angle of the fruit, fresh weight, dry weight, vertical diameter and seed yield rate of the seeds, and 76.6% of the five traits of the fruit as well as 63.0% of the four traits of the seeds were influenced by the altitude gradient.【Conclusion】Changes in the altitude caused significant changes in the climate, topography, soil and nutrient conditions. where plants live, causing plant organ traits to exhibit certain altitudinal- companied characteristics. As the altitude of the P. armeniaca population in Turgen, Xinyuan county increased, the fruit and seed sizes gradually decreased, and the fruit color, fruit quality and seed production rate gradually increased, with the altitude being closely related to fruit and seed traits, and the degree of determination being significant. These differences reflected the adaptation of reproductive inputs and survival adaptations of P. armeniaca to environmental change. Further research on the seed fate of wild fruit trees in vertical habitats will be important in exploring the self-sustaining mechanisms of P. armeniaca.